Handoff freedman


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Handoff freedman

  1. 1. Handoff in GSM/GPRS Cellular Systems Avi FreedmanHexagon System Engineering
  2. 2. Outline• GSM and GSM referemce model• GPRS basics• Handoffs – GSM – GPRS • Location and Mobility Management • Re-selection and routing update • QoS
  3. 3. 2.5 G – Provide data service• The GSM family – Basic GSM: 9.6 kbps – HSCSD: 28.8 kbps / Circuit switched – GPRS: 40 kbps – EDGE: 384 kbps• The D-AMPS/ IS-136 Family – CDPD: 9.6 kbps / 19.2 kbps – EDGE: 384 kbps• The IS-95 Family – IS-95a – 9.6 kbps – IS-95b – 115.2 kbps – IS-95c / HDR– 2Mbps
  4. 4. The Cellular Network EIR BTS External MS BTS BTS BSC MSC Networks Base Station HLR VLR Other MSC AuC Other VLRs• MS – Mobile Station • HLR – Home Location Register• BTS – Basestation Transceiver • VLR – Visitor Location Register Station • EIR – Equipment Identity Register• BSC – Basestation Controller • AuC – Authentication Center• MSC – Mobile Switching Center
  5. 5. Basic GSM reference model GCR EIR SIWF IWF External MS BTS BSC MSC GMSC Networks Base Station SIM SMS-GMSC HLR VLR SMS-IWMSC AuC SMS-SC• SIM – Subscriber Identity • GMSC- Gateway MSC Module • SMS – Short Message• GCR- Group Call Register Service• IWF – InterWorking Function • SC – Service Center• SIWF – Shared IWF
  6. 6. GSM/GPRS reference model GCR EIR SIWF IWF MSC GMSC External NetworksTE MS BSS SMS-GMSC SMS-IWMSC HLR VLR AuC SMS-SC SIM SGSN GGSN PDN • TE – Terminal Equipment • PDN – Public Data Network • SGSN – Serving GPRS Support Node • GGSN – Gateway GPRS support Node
  7. 7. GPRS Data Rate
  8. 8. GPRS Protocol Stack MAC – Medium Access Control RLC – Radio Link ControlNetwork •Backward Error Control-ARQ Network Layer •Slotted ALOHA Layer •Master-Slave conceptSNDCP SNDC GTP GTP •Capacity on demand PSPDN Specific PLL-LLC P Physical Link subLayer •Multiframe structure for PDCH TCP/UDP LLC LLC TCP/UDP Protocols •Forward Error Correcetion RLC burst BSSGP •4RLC Interleaving BSSGP IP IP RFL- RF sublayer •Link congestion detectionMAC •GSM Protocol MAC FR FR L2 L2 PLL PLL PHY PHY PHY PHY RFL RFLMS Base Station SGSN GGSN
  9. 9. GPRS Protocol Stack GTP GPRS TunnelingNetwork Network Layer Protocol LayerSNDCP SNDCP GTP GTP PSPDN Specific LLC LLC LLC TCP/UDP TCP/UDP Protocols SNDCP RLC RLC BSSGP BSSGP IP IP Sub-NetworkMAC MAC FR FR L2 L2 DependentPLL Convergence Protocol PLL PHY PHY PHY PHY RFL RFLMS Base Station SGSN GGSN
  10. 10. Handoffs in GSM and GPRS
  11. 11. GSM• Types (network elements) – Intracell HO – Inter-Cell HO within the same BSC – Intra MSC HO – Inter MSC HO• Types (function location) – Mobile initiated – Network initiated, mobile assisted
  12. 12. GSM (cont.)• Measurements of the Broadcast Channel on a free time slot• Decision according to: – Minimum acceptable performance power control is preferred over HO – Power budget algorithms HO is preferred over power control
  13. 13. GSM Handover Initiation• Initiation by the network providing – New channels characteristics – Characteristics of a new cell – Power level – Physical channel establishment procedures – Timing advance – Cipher mode setting
  14. 14. Physical Channel Establishment• Finely synchronized cells• Non synchronized cells• Pseudo synchronized cells• Pre-synchronized cells
  15. 15. GPRS Mobile Station Modes of Operation• Class A: The MS is attached to both GSM and GPRS simultaneously• Class B: The MS is attached to both but can operate in only one at a time• Class C: The MS is attached to GPRS or other GSM services
  16. 16. Cell Hierarchy Location AreaLocation Area Routing Area RA RA RA
  17. 17. Levels of Location Management• Cell Update (re-selection procedure) – Originated by MS – Based on BCCH measurements – Other criteria may apply• Routing Area update – Initiated by mobile when crossing RA boundary
  18. 18. Mobility Management States• Idle – MS is not attached to GPRS• Standby – Subscriber is attached to GPRS mobility management – MS performs RA and cell selection locally, reports RA changes – Data, signaling or page response move the MS to READY – Detach procedures moves the state to Idle• Ready – Information on cell selection is reported – Cell selection may be done locally or by network control – State supervised by a timer
  19. 19. Mobility Management States
  20. 20. GPRS Re-Selection• GPRS IDLE state and wishes to initiate the GPRS Attach procedure: – If the currently camped-on cell supports GPRS then no cell reselection is required. – If the currently camped-on cell does not support GPRS, then reselection of a cell supporting GPRS is required before execution of the attach procedure.• If the MS is in GPRS STANDBY or READY state, cell selection and reselection procedures specific to GPRS shall be used• The cell reselection procedure used in READY state shall minimise the cell changes.• If the MS is in dedicated mode, then the changes from one cell to another is performed according to the network-controlled handover procedures.• There may be co-ordination of the idle and dedicated mode procedures used for circuit-switched services with the READY state procedure for MSs that are both IMSI-attached and GPRS- attached.
  21. 21. Routing Update Procedure • MS sends RA update request containing the cell identity and the identity of previous routing area, to new SGSN • New SGSN asks from old SGSN the context (GGSN address and tunneling information) of the MS • New SGSN updates GGSNs, new SGSN address and tunneling information is delivered to GGSN • New SGSN updates HLR • HLR cancels the MS information context in old SGSN • HLR loads the subscriber data to new SGSN • New SGSN acknowledges to the MS • The previous SGSN is requested to transmit the undelivered data to the new SGSN.www.ece.wpi.edu/~prashant/geo/neth98.pdf
  22. 22. QoS Profiles• Precedence Class – High, Normal, Low• Delay Classes• Reliability Classes• Throughput classes
  23. 23. Delay Classes
  24. 24. Reliability Classes
  25. 25. Reliability Classes (cont.)
  26. 26. Peak Throughput Class
  27. 27. Mean Throughput Classes
  28. 28. Handoff Summary• No special probe signal is used by BTS (MCHO)• Several principles are used for handoff decision• Only passive scanning at MS is employed to detect nearby BTS (like in GSM)• In network layer MS communicates with SGSN, in physical layer with a BSS.• Several protocols and channels are employed for indicating the MSs current location
  29. 29. 802.11 GSM/GPRS CDPD Beacon Same physical Separate Physical Separate channel Channel Physical Channel Handoff Mobile GSM- BSC Mobile Decision GPRS- MSInformation to IAPP GSM – by BSC Message from old AP GPRS – by SGSN MHF to MSF of old BS Channel At the terminal At the terminal At the terminal Monitoring Access and CSMA TDMA DSMA/CD Monitoring Monitored all the Monitored when Monitored all time MS does not the time transmit or receive
  30. 30. Conclusion• Wireless data has been considered since early days of cellular technology• GSM/GPRS supports packet data together with CS traffic, with rates up to 171kbps• Handover in GPRS is strongly aligned to GSM handover• QoS is the main issue in handover of GPRS. The standard supports a variety of profiles• HO principles are similar in various types of systems